India enters supercritical
power plant technology
Variable speed drive technology: Guarantor for economic
and efficient boiler feed pump drive operation
Alexander Schust, Area Manager, Voith Turbo GmbH & Co. KG, Germany
Wolfgang Sautter, General Manager Sales, Voith Turbo GmbH & Co. KG, Germany
Presented at Power Gen India & Central Asia, New Delhi 2008
1. Status quo on power station unit sizes and
boiler feed pump drive configurations within India
Power station unit size [MW]
Drive configuration on boiler feed pumps within Indian power market
135
2 x 100% electric motor driven boiler feed pumps with geared variable speed couplings
210
3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings
250
3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings
300
3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings
500
2 x 50% steam turbine driven boiler feed pumps
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit
600
2 x 50% steam turbine driven boiler feed pumps
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit
660
2 x 50% steam turbine driven boiler feed pumps
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit
800*
2 x 50% electric motor driven boiler feed pumps with geared variable speed couplings
Figure 1: Configurations on boiler feed pump drives depending on unit sizes within India
* Future concept; not yet executed within India
With the first steps into supercritical
power plant technology India is
entering a new era in unit sizes for
power stations from 600 to 1,000
MW. When having a first look into
existing Indian power stations it is
possible to basically divide up the
Indian power market by unit sizes
and further down on the boiler feed
pump drive configurations as shown
within figure 1 above.
2
State of the art within India is the
use of steam turbines on boiler feed
pump drives for unit sizes of 500
and 600 MW. The traditional concept to be followed within this power
stations is 2 x 50% steam turbine
driven boiler feed pumps with
1 x 50% electric motor driven boiler
feed pump operated by a geared
variable speed coupling as a startup and stand-by unit. For plants
smaller than 500 MW, steam turbine
drives are not seen anymore due to
high capital cost and high efforts on
maintenance to be taken. Thus,
only electric motor drives are to be
used either with 2 x 100% or
3 x 50% boiler feed pump drive configurations depending on specific
unit sizes. All over the world, the
trend goes towards unit sizes bigger
than 500 MW.
Correspondingly, also within India a
drift to higher plant output is currently under planning and execution.
Barh and Sipat supercritical projects
of 3 x 660 MW each under NTPC
are in an advanced stage of execution. Ultra mega power projects
(UMPPs) of 4,000 MW total output
are progressing fast towards realisation. The first one is Mundra with
a plant output of 5 x 800 MW for
Tata Power Company Limited which
is currently in the execution phase.
Sasan and Krishnapatnam are the
next projects in line already secured
by Reliance Energy Limited. With
this background it is worth to take a
brief general look into currently ongoing power station projects throughout the world which will form part of
the following paper section.
2. New ongoing power projects worldwide
Power station name
Datteln 4
Staudinger
Scholven
Massflakte NL
Neurath
Hamm
Ensdorf
Enshafen NL
Unit size [MW]
1,000
1,100
1,100
1,100
1,100
800
800
800
Boiler feed pump drives configuration
1 x 100% steam turbine driven boiler feed pump
2 x 50% electric motor driven boiler feed pump with geared variable speed coupling
or 2 x 40% as start-up and stand-by unit
Walsum
790
2 x 50% electric motor driven boiler feed pump with geared variable speed couplings
Karlsruhe RDK 8
920
2 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets
Moorburg
800
2 x 50% electric motor driven boiler feed pump with variable frequency drive
Figure 2: Selection on new power station projects and boiler feed pump drive configurations in Europe
Within Europe current power station
projects with a power range exceeding 600 MW can be divided up into
power stations following the traditional concept of running a 1 x 100%
steam turbine driven boiler feed
pump in combination with 2 x 40%
or 50% electric motor driven boiler
feed pumps with geared variable
speed couplings as start-up and
stand-by units and several power
station projects following new concepts of running the main boiler
feed pumps purely on an electric
basis without the use of a steam
turbine on the main boiler feed
pump drives. The concept to be
followed will be 2 x 50% or 3 x 50%
electric motor drives. In these
electric motor driven configurations
either geared variable speed couplings, variable speed planetary
gears or sometimes variable frequency drives are being used. The
table above gives a selection of
several European power station
projects showing the basic concepts
to be followed on these power
stations.
3
Power station name
Unit size [MW]
Boiler feed pump configuration
Rodemacher
Spruce
600
750
1 x 100% steam turbine driven boiler feed pump
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up
and stand-by unit
Iatan
Trimble County
850
735
2 x 50% steam turbine driven boiler feed pumps
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up
and stand-by unit
Nebraska City 2
Plum Point
600
665
2 x 50% electric motor driven boiler feed pump with geared variable speed couplings
Longview
Dominion City
600
585
3 x 50% electric motor driven boiler feed pump with geared variable speed couplings
Weston
500
3 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets
Figure 3: Selection on new power station projects and boiler feed pump drive configurations in the USA
Within the US market, the traditional
concept mainly followed in the past
was a 1 x 100% steam turbine driven boiler feed pump and for start-up
and stand-by purposes a 1 x 2550% electric motor driven boiler
feed pump arranged with a geared
variable speed coupling. Also today
with new power station projects of
more than 500 MW unit size, this
concept is still to be seen but also
Power station name
Unit size [MW]
within the US market a trend
towards the use of electric motor
drives only as main boiler feed
pump drives is noticeable as per
table shown above.
Looking into the Chinese power market the traditional concept followed
for several 600 MW units is 2 x 50%
steam turbine driven boiler feed
pump drives with 1 x 30% electric
motor driven boiler feed pumps operated with a geared variable speed
coupling as a start-up and stand-by
unit. However, new power station
projects within China are also leaning more and more to electric motor
drives only without steam turbines
as per the following table.
Boiler feed pump configuration
Zhaoguang
Ningxia
Yuncheng
Minquan
600
600
600
600
2 x 50% steam turbine driven boiler feed pump
1 x 30% electric motor driven boiler feed pump with geared variable speed coupling as start-up
and stand-by unit
Hancheng
Fenhzhen
Hequ
DaLaTe
600
600
600
600
2 x 50% electric motor driven boiler feed pumps with geared variable speed coupling
1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up
and stand-by unit
Pucheng
600
2 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets
1 x 30% electric motor driven boiler feed pump with geared variable speed coupling as start-up
and stand-by unit
Figure 4: Selection on new power station projects and boiler feed pump drive configurations in China
4
3. Resulting effects on Indian power station projects
Figure 5: Specification text for boiler feed pump package
for 5 x 800 MW UMPP Mundra, India
The trend towards the utilisation
of pure electric motor drives only
already influences ongoing Indian
power station projects. In 2007,
Tata Consulting Engineers specified
electric motor drives only without
any start-up and stand-by units for
5 x 800 MW UMPP Mundra. The
paragraphs of the specification
shown above give the wording used
to specify this concept in order to
put India also in line with the worldwide ongoing trend.
Besides the first big step in entering
into new supercritical power plant
technology within India additionally
another big step forward is taken at
the same time when specifying and
executing drive packages as per
package No. 1 above without the
use of a steam turbine on the main
boiler feed pumps and without the
use of any start-up and stand-by
units. These huge steps taken into
further development of Indian power
Figure 6: Specification text for boiler feed pump drives
for 5 x 800 MW UMPP Mundra, India
plant technology will influence further upcoming projects within India
and will set new standards within
power station unit sizes, drive technologies in terms of plant efficiency,
cost impacts and reliability issues.
By going to a 2 x 50% boiler feed
pump arrangement without stand-by
unit, the reliability of the boiler feed
pump trains is of utmost importance. Thus, reliability of each component of the drive train has to be
evaluated with a special focus on
the variable speed drive system
itself. Therefore most power plants
around the world using this 2 x 50%
configuration have decided to use
hydrodynamic variable speed drives
due to its superior reliability. The
key factor is to be really seen as
highest required reliability on the
drive systems used on the boiler
feed pump drives in order to not
affect the plant output. As a result
of this insight Tata Consulting
Engineers specified hydrodynamic
drives on the boiler feed pumps.
This is shown within the following
specification text where Tata Consulting Engineers specified geared
variable speed couplings only. Also
it can be noted that Tata Consulting
Engineers specified the first time
ever within India the highly efficient
variable speed planetary gear drive
as an option to the conventional
geared variable speed couplings
also shown in the specification text
above.
With this common trend towards
electric motor drives all over the
world it is now worth to take a closer look into the different boiler feed
pump configurations with electric
motors only. This will form part of
the next paper section.
5
4. Boiler feed pump drive configurations
for electric motor drives
Option (A)
3 x 50% GVSC
Option (B)
2 x 50% GVSC
Figure 7: Electric motor drive configurations on boiler feed pumps
GVSC Geared Variable Speed Turbo Coupling
VSPG Variable Speed Planetary Gear Set
For electric motor drives on boiler
feed pumps it can be distinguished
between drive configurations as per
chart given above within figure 7.
6
Option (A) is reflecting the traditional concept with a configuration
where 2 x electric motors run 2 x
main boiler feed pumps supplying
feed water into the boiler. Both
boiler feed pumps are operated on
variable speed with a geared variable speed coupling installed in the
drives. Additionally, an electric
motor drive facilitates the start-up
procedure by filling the system with
water and serves as a stand-by unit
in case one of the boiler feed
pumps trips. This stand-by unit is
also operated as a variable speed
pump via a geared variable speed
coupling. Having the additional
stand-by unit provided, this drive
configuration displays together with
option (C) the most safe way to operate the plant and in addition to
that, in any case a more economic
way as by utilising a steam turbine
in the drive.
Option (B) is probably the most
modern and as a matter of fact,
most economic drive configuration.
Especially for tariff based bidding
processes, this is the most attractive solution. This system is introduced within India on 5 x 800 MW
UMPP Mundra where 2 x 50% main
boiler feed pumps are proposed to
be driven via geared variable speed
couplings by electric motors only.
For this specific drive configuration
no stand-by unit is specified leading
to the necessity that the installed
drives are required to prove for
highest reliability throughout the
complete lifetime of the plant.
Having no steam turbine and additionally saving the money in cutting
down the investment for a separate
stand-by unit, this drive configuration reflects by far the most
economic drive system in power
utilisation.
Option (C)
2 x 50% VSPG +
1 x 30% GVSC
Option (C) fitted with variable
speed planetary gear sets on the
main boiler feed pumps offers the
highest drive efficiencies – of
course on the basis of higher initial
costs – also resulting in a better
plant efficiency than drive configurations as per options (A) and (B).
High drive efficiencies are especially inherent to the variable speed
planetary gear set and are put into
place most effectively when operating at variable plant loads. This
advantage of high drive efficiency
with the variable speed planetary
gear set is especially paid off
against other drive systems used.
Having additionally a stand-by unit
installed on the drive configuration
for option (C) this option reflects a
compromise between options (A)
and (B) for electric motor driven
boiler feed pump drives. As the
stand-by unit is designed smaller
than as for option (A), the investment for this unit within option (C) is
more attractive than within option
(A). In case of a failure of one of the
main pump trains almost full plant
load can be achieved with the
stand-by unit. The additional investment on the variable speed planetary gear sets within option (C) over
option (A) with geared variable
speed couplings installed on the
main boiler feed pump drives will
certainly pay back due to high efficiency of the drive systems inherent to it. Thus, option (C) displays
an agreement in both, satisfying
a safety-oriented plant philosophy
in having a separate stand-by unit,
as well as economically offering the
most competitive solution with
regard to drive systems with steam
turbines or traditional 3 x 50%
electric motor driven units installed
on the drive systems.
As all these drive configurations are
based on hydrodynamic variable
speed drives it is now time to look
into this specific technology more
closer.
7
5. Facts about hydrodynamic turbo couplings
and variable speed drive systems
1
2
3
1
2
3
6
8
5
Figure 8: Foettinger Principle as a basis
for hydrodynamic turbo couplings
Figure 9: Sectional view of a hydrodynamic
variable speed turbo coupling
1 Impeller (primary wheel)
2 Circulating operating fluid
3 Turbine wheel (secondary wheel)
1
2
3
4
5
6
7
8
Hydrodynamic turbo couplings are
based on the Foettinger Principle
where the input power developed
by a prime mover is converted from
mechanical energy acting on the
impeller (primary wheel) into kinetic
energy within the operating fluid
and converted back into mechanical
energy at the turbine wheel (secondary wheel) connected to the
driven machine.
8
Impeller (primary wheel)
Turbine wheel (secondary wheel)
Shell
Scoop tube housing
Oil tank
Oil circulation pump
Scoop tube
Oil cooler
To get variable speed on the driven
machine, the oil filling of the hydrodynamic turbo coupling has to be
regulated. An additional component,
a so-called scoop tube, installed
into the hydrodynamic turbo coupling allows the adjustment of the
working oil filling inside the coupling
while in operation. This reflects a
hydrodynamic variable speed turbo
coupling.
4 7
1
9
Variable speed offers …
6
11
10
7
reduced energy consumption
= energy and cost savings
process adaptation
= reduced emissions and less pollution
load pattern orientation
= increased flexibility by orientation on actual plant output
speed adaptation
= increased service life of installed equipment
and in addition hydrodynamic variable speed drives offer …
12
simple robust mechanical design = reduced maintenance requirements
5
2
8 3
4
Figure 10: Sectional view of a hydrodynamic
variable speed coupling with integrated gear stage
1
2
3
4
5
6
7
8
9
10
11
12
highest availability and reliability
= process stability
compact design
= less space needed, less investment costs
load free motor start-up
= start-up possible under bad power grid conditions
vibration dampening features
= shocks from motor or driven machine are not transmitted
integrated lube oil system
= no additional separate lube oil system needed
Figure 11: Benefits of variable speed and
hydrodynamic variable speed drives
Gear stage
Hydrodynamic variable speed turbo coupling
Scoop tube
Electro-hydraulic positioning control (VEHS)
Working oil cooler
Lube oil cooler
Main lube oil pump
Oil circulation control valve
Working oil pump
Auxiliary lube oil pump
Reversible duplex filter
Oil reservoir
For typical boiler feed pump drives
running at high output speeds of approximately 5,000 rpm to 6,000 rpm
hydrodynamic variable speed turbo
couplings can be combined with
one or more gear stages in a common housing.
As all these drives act on the same
basic operational principle they all
imply the same advantages belonging to hydrodynamic power transmission technology. In addition all
benefits common to variable speed
drive systems are also realised
when installing these drives. An
overview on these benefits is given
within figure 11 above.
9
D
A
B
C
Pu ⬃ 25%
Pe
Figure 12: Sectional view of a hydrodynamic variable speed planetary gear set and principle of power splitting
Variable speed planetary gear set
A Hydrodynamic torque converter
B Stationary planetary gear
C Revolving planetary gear
D Oil supply system
Due to physical laws, efficiency of
the drives as described before decreases as the output speed of the
drive systems goes down. To come
around this, the variable speed
planetary gear set used within drive
configuration (C) of section 4.) of
this paper introduces the principle
of power splitting into variable
speed drives technology. Within its
10
Variable speed planetary gear set
Principle of power splitting
Pe Input power
Pu Superimposing output
Pa Output power
components the variable speed
planetary gear set consists of one
or more hydrodynamic circuits in
combination with mechanical gears
as per each individual application
required. Figure 12 illustrates the
setup of the individual components
of the hydrodynamic variable speed
planetary gear set and the principle
of power splitting applying to it.
⬃ 75%
Pa
100
A
Efficiency [%]
80
B
60
40
0
0
20
40
60
80
100
Load [%]
Figure 13: Efficiency curves of hydrodynamic variable speed drives
A Variable speed planetary gear set
B Geared variable speed coupling
Within this power splitting principle,
the majority of power is transmitted
mechanically, directly via the main
shaft and the rotating planetary
gear. Only that portion of input power necessary for speed adjustment
of the driven machine is split from
the main shaft via the adjustable
hydrodynamic torque converter and
superimposed on the rotating planetary gear set. Due to the high
portion of mechanically transmitted
power, the entire unit has an efficiency of over 95% over a wide
operating range as shown in figure
13 of this paper.
11
C
Ne
Ne
Nu
Nu
Na
Na
Figure 14: Output speed variation with a variable speed planetary gear set
Variable speed planetary gear set
C Revolving planetary gear
Within the hydrodynamic variable
speed planetary gear set the output
speed is controlled by adjusting the
superimposed speed. The maximum superimposed speed results in
the highest output speed. A reduction or reversal of the superimposed
speed results in a reduced output
speed. This is shown within figure
14 above.
Ne Input speed
Nu Superimposed speed
Na Output speed
Ring gear
Planet
Planet carrier
Sun gear
3-D-view of revolving planetary gear
12
Vorecon type RW
boiler feed pump, Germany
Power 8,500 kW
Speed 5,000 rpm
A
1
2
3
Figure 15: Set-up of a hydrodynamic torque converter as part of the variable speed planetary gear set
Variable speed planetary gear set
A Hydrodynamic torque converter
The superimposed speed itself is
varied by adapting the oil flow
inside the hydrodynamic torque
converter by operating and adjusting internal guide vanes. Figure 15
above shows the location of the
hydrodynamic torque converter (A)
inside the variable speed planetary
gear set as well as its setup.
Hydrodynamic torque converter
1 Adjustable guide vanes
2 Pump wheel
3 Turbine wheel
As now the technique applying to
hydrodynamic variable speed drives
is systematically illustrated, the
upcoming paper section focuses
especially on the commercial
assessment of these drives.
13
6. Commercial evaluation on different
variable speed drive systems
VSPG
⬃ 45 m2
Motor
VSPG
Motor
Gear
Cooling
system
VFD
⬃ 150 m2
Harmonic
filter
Isolation
transformer
Oil
system
Cooling
system
Frequency
drive
Figure 16: Comparison in field conditions of different variable speed drive systems
VSPG Variable speed planetary gear
VFD
Variable frequency drive
To find the most economical drive
system, a thorough analysis of lifecycle cost has to be done. This
analysis should include equipment
cost, installation and infrastructure
cost, commissioning and maintenance cost as well as energy cost.
14
The variable speed planetary gear
drive system is very simple and requires few components, compared
to a variable frequency drive system
as shown within figure 16 above.
This results in less required space,
less cost for setting up buildings
and more simple installation and
commissioning.
Equipment cost are significantly
lower, especially for high power applications. Due to the high reliability
of the variable speed planetary
gear drive system, maintenance
and repair cost are extremely low.
Overhead
tank
13.8 kV
Motor
losses
VSPG
losses
Motor
VSPG
Working
machine
Power for
cooler (fans)
Transformer VFD
losses
losses
Motor
losses
Gear
losses
Motor
Gear
Working
machine
VFD
13.8 kV
Optional input
filter losses
Filter
losses
Power for
cooling system
Power for
air conditioning
Power for
cooler (fans)
Power for
oil system (pumps)
Figure 17: Systemic efficiency line-up of different variable speed drive systems
VSPG Variable speed planetary gear
VFD
Variable frequency drive
Furthermore, energy cost for the
variable speed planetary gear set is
similar to a variable frequency drive
when a sound evaluation in comparing the entire drive system is done.
For this purpose it has to be ensured that all relevant component
efficiencies are included in the
considerations.
Figure 17 illustrates that with a variable frequency drive system a lot
more drive components are set in
place reducing drive efficiency than
as for the variable speed planetary
gear set. All these different additional drive components imply additional power losses with the result
of more energy consumed for the
variable frequency drive system.
15
Load pattern
(4 x 800 MW)
Operating points
Summer
75%
100%
MCR 100%
BMCR 103%
BMCR 103%
Design Point
Point A
Point B
Point C
Point D
Point E
Point F
500
500
7,000
10
10
5
Power consumption of pump (kW)
4,463
6,652
11,164
11,842
12,963
13,382
Operating speed (rpm)
3,663
4,131
4,804
4,890
5,008
5,069
Motor efficiency
97.0%
97.3%
97.7%
97.7%
97.7%
97.7%
VFD efficiency
96.5%
97.0%
97.5%
97.5%
97.5%
97.5%
Transformer efficiency
99.0%
99.0%
99.0%
99.0%
99.0%
99.0%
Isolation transformer efficiency
99.0%
99.0%
99.0%
99.0%
99.0%
99.0%
Gear box efficiency
98.0%
98.2%
98.5%
98.5%
98.5%
98.5%
Overall efficiency
89.9%
90.8%
92.0%
92.0%
92.0%
92.0%
Operating time (hours per year)
Drive
system
efficiency
& electrical power
consumption
VFD
Electrical power consumption (kWh/a)
VSPG
2,481,998
3,661,473
84,979,089
128,771
140,961
72,759
Lube oil pump (30 kW estimated)
15,000
15,000
210,000
300
300
150
Motor efficiency
97.2%
97.5%
97.9%
97.9%
97.9%
97.9%
Vorecon efficiency
86.2%
87.8%
94.8%
95.1%
95.1%
94.9%
Transformer efficiency
99.0%
99.0%
99.0%
99.0%
99.0%
99.0%
Overall efficiency
82.9%
84.7%
91.9%
92.2%
92.2%
92.0%
2,690,222
3,924,532
85,053,393
128,477
140,639
72,746
193,225
248,060
-135,695
-594
-622
-163
0.03
0.03
0.03
0.03
0.03
0.03
Savings per year in Euro
5,797
7,442
-4,071
-18
-19
-5
Total savings (S) with VFD per year
9.126 Euro
Electrical power consumption (kWh/a)
Energy
savings
with
VFD system
Power savings with VFD system (kWh/a)
Power cost (Euro/kWh)
Investment VFD
VSPG
Payback
calculation
Estimated VFD system cost
Price VSPG
VFD
1,600,000 Euro
Gear
150,000 Euro
Oil supply system
90,000 Euro
Extra price motor
50,000 Euro
Wiring
80,000 Euro
Total
1,970,000 Euro
VSPG
950,000 Euro
Difference in cost (C) Euro
1,020,000
Interest rate (i) %
8%
Cost increase (f) %/a
Payback formular
3%
N = log (r/(r-i)/log (1+i)
Payback rate
Payback rate r = (S-C*f)/C
Payback time
-21 years, 7 months
Figure 18: Example of a payback calculation for different variable speed drive systems
VSPG Variable speed planetary gear
VFD
Variable frequency drive
16
-0.021052647
Best to illustrate economic advantages of hydrodynamic variable
speed drive systems over variable
frequency drive systems is to perform an objective payback calculation evaluating the different drive
efficiencies as well as the difference
in investment cost for the evaluated
drive systems. Figure 18 shows
this exemplarily for a power station
convoy of 4 x 800 MW.
The load pattern of the power plant
is the basis for the evaluation and is
used to calculate the electrical power consumption in kWh/a for the
different drive systems looked into.
On doing so, it is absolutely essential to evaluate the different drive
systems on the basis of all components installed as pointed out
above. It has to be a systemic view,
each drive system has to be evaluated in total, not just in its single
components only. For the evaluation done within figure 18, energy
cost for the variable frequency drive
system are less than for the variable speed planetary gear set due to
having slightly better overall efficiency values for the given load
pattern. This leads to total energy
savings of Euros 9,126.00 per year
when operating the variable frequency drive system. To complete
the economic evaluation, the investment side has to be considered
resulting in a payback calculation to
be performed. Based on a certain
interest rate and cost increase per
year, a net present value calculation
incorporates the total energy savings calculated in combination with
the difference in investment cost
between the different variable
speed drive systems. With the variable speed planetary gear drive, the
initial cost are much lower than with
the variable frequency drive system
with its advantages in cost savings
on the energy side. Thus, even with
money being saved on the energy
side, the variable frequency drive
system will not pay back due to
having a negative payback calculated. The higher investment cost of
the variable frequency drive system
cannot be recovered, not even in a
20 or more years plant life.
The outcome of this payback calculation shows the advantages of the
hydrodynamic variable speed drive
in being the most competitive drive
system. In combination with drive
configuration (B) or (C) of section 4
of this paper, tariff-based project
bids can be viewed as best served
when installing hydrodynamic variable speed drive systems due to
being able to offer real economic
advantages to utility companies and
power station owners.
17
7. Conclusion
Reliability figures of hydrodynamic variable speed drives
(based on data available on variable speed planetary gear drives)
No. of units evaluated
69
Power range [kW]
600 - 11,931
Output speed [rpm]
495 - 16,482
Total operating hours
2,095,921
No. of reported failures
6
Non availability time [hrs]
546
Reliability calculation:
(2,095,921 - 546) / 2,095,921 = 99.97 %
(based on machines in operation)
MTBF calculation:
2,095,921 / 6 = ~ 39 years
(based on machines in operation)
Figure 19: Reliability figures of hydrodynamic variable speed drives (variable speed planetary gear drives)
On the background of the ongoing
trend towards higher plant output
combined with tariff-based project
bidding systems the ambition towards a most economic operation
of a power plant plays a vital role for
successfully running a state of the
art power station. Within this, hydrodynamic variable speed drives are
able to offer all its inherent success
factors to utility companies and
power station owners. Objective
payback calculations give proof of
that.
18
Operating a hydrodynamic variable
speed drive system realises all
advantages which belong to variable speed drives in general in
combination with all success factors
essential to hydrodynamics as the
operational principle of the drive
systems. In this respect, more
flexibility offered by the use of the
hydrodynamic variable speed drive
system means highly efficient and
environmental-friendly processes
can be realised while saving money
at the same time. Thus, efficiency of
the drive systems used has to be
seen as yet another success factor
a drive system should be evaluated
on. Objective efficiency comparisons performed on a systemic view
are able to give evidence of this.
Durability of the drive system installed has to be seen as a further
success factor of essential interest
to the utility companies aspiring a
most satisfactorily operating plant.
A drive system shall be designed
for a minimum of the life time of the
whole plant, thus, a minimum of at
least 25 years of operation should
be considered as basis for a drive
evaluation. This means a minimum
of at least 25 years of operation
where spare parts availability has to
be ensured. The technology used
has to be long-lasting, not rapidly
changing. Proven mechanical components still being available within
30 years from today form the basis
of a trustworthy alliance to a hydrodynamic variable speed drive
system on which this can easily be
proven for.
=
Efficiency
VFD
versus
VSPG
Economics
Reliability
Durability
Figure 20: Success factors for evaluation of variable speed drive systems
VSPG Variable speed planetary gear
VFD
Variable frequency drive
Highest reliability of the drive system acts as the basis for longest
operating hours to be realised for
economic plant operation. Downtime of the plant is most cost-intensive and has to be avoided in order
to ensure smooth production.
Availability is the most critical factor
when calculating the life-cycle cost
of an installation. Using a hydrodynamic variable speed drive
system proves for a reliability of
99.97% or in other words, an MTBF
of more than 39 years based on
machines in operation as shown
within figure 19 can be adhered to.
In pursuing the optimum solution for
each individual power station
project, it becomes clear that an objective assessment of different drive
systems has to be done on the basis of 4 essential success factors as
shown in figure 20 above.
䡲 Drive reliability counts as
nothing can compensate for lost
production.
䡲 Drive economics count as only
the most economic system
will sustain thorough payback
evaluations done.
䡲 Drive durability counts as only a
constant running system proves
for the economic figures being
expected.
䡲 Drive efficiency counts as only
adapted processes to be run help
saving money.
On this background it becomes
clear that all four success factors
have to interlock into each other
in order to develop an overall drive
system evaluation showing the
optimum solution to the decisionmakers. Considering a hydrodynamic variable speed drive system within such an evaluation will,
in all respects, surely pay back.
19
Voith Turbo Private Limited
P.O. Industrial Estate
Nacharam
Hyderabad – 500 076
Tel: +91 40-27 17 35 61, 27 17 14 40
Fax: +91 40-27 17 11 41, 27 17 31 34
info.hyd@voith.com
www.voithturbo.com
Cr 605 en, 04.2009, aik / SVG, 600. Printed in Germany. Subject to modification due to technical development.
Voith Turbo GmbH & Co. KG
Variable Speed Drives
Voithstr. 1
74564 Crailsheim, Germany
Tel: +49 7951 32-261
Fax: +49 7951 32-650
vs.drives@voith.com
www.voithturbo.com/variable-speed